Nucleonic measuring apparatus with automatic fire safety radiation source shutter closing and locking means controlled by a fusible element which melts at high temperatures

ABSTRACT

A nucleonic measuring instrument wherein a housing contains a radiation source and has an aperture controlled by a shutter which is spring loaded to a closed position for confining and shielding the radiation and is movable by a linear actuator to an open position for releasing the radiation, the actuator power being applied through a heat sensitive fuse so that it is deenergized and the shutter closes in response to a predetermined high ambient temperature such as may be caused by a fire, and including a spring-biased shutter locking pin retained in a retracted position by a meltable metal barrier which melts to release the pin in response to attainment of a predetermined higher ambient temperature and lock the shutter in the closed position.

United States atent Richard E. Bach Hilliard, Ohio Apr. 27, 1967 Mar. 2,1971 Industrial Nucleonics Corporation Inventor Appl. No. Filed PatentedAssignee NUCLEONIC MEASURING APPARATUS WITH AUTOMATIC FIRE SAFETYRADIATION SOURCE SHUTTER CLOSING AND LOCKING MEANS CONTROLLED BY AFUSIBLE ELEMENT WHICH MELTS AT HIGH TEMPERATURES Primary Examiner-RalphG1 Nilson Assistant Examiner-Morton J. Frome AttorneysMarechal, Biebel,French & Bugg, William T.

Fryer, III, C. Henry Peterson and James .I. OReilly ABSTRACT: Anucleonic measuring instrument wherein a housing contains a radiationsource and has an aperture controlled by a shutter which is springloaded to a closed position for confining and shielding the radiationand is movable by a linear actuator to an open position for releasingthe radiation, the actuator power being applied through a heat sensitivefuse so that it is deenergized and the shutter closes in response to apredetermined high ambient temperature such as may be caused by a fire,and including a spring-biased shutter locking pin retained in aretracted position by a meltable metal barrier which melts to releasethe pin in response to attainment of a predetermined higher ambienttemperature and lock the shutter in the closed position.

PATENTED "AR 2 I97! SHEET 1 OF 2 0 W M A n B A. a M D R m m R v! 8 H6 3O 6 a 5 5 NUCLEONIC MEASURING APPARATUS WITH AUTOMATIC FIRE SAFETYRADIATION SOURCE SHUTTER CLOSING AND LOCKING MEANS CONTROLLED BY AFUSIBLE ELEMENT WHICH MELTS AT HIGH TEMPERATURES RELATED INVENTIONSBACKGROUND OF THE INVENTION Nucleonic measuring gauges have beenprovided with source housings having apertures controlled by shutterswhich are operated by an electric solenoid or by an air motor, or thelike, for retracting and permitting the release of the radiation from asuitable nucleonic source within the housing. Examples of such shuttersare shown in the US. Pat. No. 2,858,450 ofv 1958 to Holben and US Pat.No. 2,932,744 of 1960 to Lehman, each assigned to the assignee of thisinvention. These shutters are normally made of heat resistant materialand also act as an effective block or shield for the rays emanatingfromthe source, so that when the shutter is closed, the source cap-. sule iseffectively sealed within-its housing and no substantial radiationemanates through the aperture.

Normally, the shutter mechanism are fail-safe so that upondeenergization of the operating motor, the shutter automatically returnsto the closed position such as by the'use of retraction springs or thelike. In the event of a disaster or conflagration, it is important tomaintain the integrity of the source housing and to confine allradiation within the housing; This is accomplished by assuring that theshutter returns to the closed position under such conditions and remainsthere.

SUMMARY OF THE INVENTION The present invention relates to nucleonicgauging and measuring apparatus, and more particularly, to suchapparatus in which a movable shutter is positioned in relation to theexit aperture for a nucleonic source, and to apparatus for closing andlocking the shutter in the event that certain predetermined temperaturelimits are exceeded.

The invention employs motor means, such asan electric solenoid, formoving the shutter between a closed positionwhere it effectively shieldsradiation from the source of radioactive material and an open positionwhere the aperture is uncovered. Normally, during the operation of thegauge, the shutter is maintained in its open position with respect tothe aperture, by continuously energizing the solenoid. However, it iswithin the scope of this invention to use other means such as anair-operated motor shown in the Holben and Lehman patents mentionedabove.

The invention further includes means responsive to the occurrence of afirst predetermined temperature for causing the shutter to close andseal the source capsule within its housing to render it relativelyharmless in the event of fire or the like. This means includes atemperature responsive element, such as a fuse, to interrupt the powerto the solenoid so that the shutter is returned to its closed positionby the shutter retraction springs.

The present invention also provides for locking the shutter in theclosed position upon the occurrence of a still higher predeterminedtemperature, and specifically employs a pin which is spring loaded in aretracted position where it is retained by a solder barrier. The barrieris adapted to melt when a predetermined ambient temperature occurs andthereby release the pin to engage and lock the shutter in its closedposition.

Thus as a primary, object, the present invention provides a nucleonicgauge with a shutter which moves to a closed position upon theoccurrence of a high ambient temperature and which is thereafter lockedin its closed position by a locking member which becomes operative inresponse to the melting of a solder barrier with the occurrence of astill higher ambient temperature.

A more specific object of this invention is the provision of a shutterfor a nucleonic source housing and which is opened against the bias ofsprings by an operator which becomes deenergized with the occurrence ofabnormally high heat, and a spring loaded pin is released when theambient temperature further increases to the melting temperature of asolder barrier and thereby locking the shutter in its closed position.

These and other objects and advantages of the invention will be apparentfrom the following description, the accompanying drawings and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of anucleonic thickness gauging system including a shutter assembly and lockconstructed in accordance with the invention;

FIG. 2 is an elevational viewof the radiation source head partiallybroken away;

FIG. 3 is a view of the shutter assembly and its operating mechanism astaken generally on the line 3-3 of FIG. 5;

FIG. 4 is a section taken generally on the line 4-4 of FIG. 3;

FIG. 5 is a bottom view ofthe apparatus shown in FIG. 3;

FIG. 6 is a fragmentary section of the shutter lock as taken generallyon the line 6-6 of FIG. 3 and taken before the lock is released;

FIG 7 is a fragmentary section similar to FIG. 6 and showing the shutterlook after it is released;'

FIG. 8 is a fragmentary section taken generally ontthe line 8-8 ofeither FIG. 5 or 6; and

FIG. 9 is a fragmentary section showing the interlocking-of the shutterand its supporting plate.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a nucleonicthickness measuring gauge 10 is connected to an electronic equipmentcabinet 12- through flexible cables 13 and an intermediate disconnectbox, 14. A conduit 15 leads from the cabinet 12 to a combined recorderand remote control unit 16 located at an operators station.

The thickness measuring gauge 10 may be of any suitable type utilizingradioactive material as the source, and may be constructed as shown inChope U.S.'Pat. No. 2,790,945 of 1957 and US. Pat. No. 2,829,268 of1958, both assigned to the same assignee as this invention. Furthermore,it is within the scope of this invention to employ a backscatter gaugeas shown in the above mentioned Holben patent.

As shown in FIG. 1, the gauge 10 includes a C-shaped frame 20 having anupper leg 21- and a lower leg 22 supported by a carriage 23 mounted fortraversing movement on a supporting rail 24. A housing 25 is mounted onthe rail 24 and encloses a motor which is connected to move the frame 20in directions as indicated by the arrow 26.

.A radiation source head 30 is mounted on the lower leg 22 of the frame20 and a detector head 31 is mounted on the upper leg 21 directly abovethe head 30. The heads 30 and 31 cooperate to form a gap or spacethrough which a traveling web W of material is directed. Referring toFIG. 2, the source head 30 includes a member 33 supporting a plate34.which forms a cover for a cylindrical shaped housing 35 containing aradiation source 36. The plate 34 has a U-shaped opening or aperture 37(FIG. 3) through which the radiation is directed upwardly towards thedetector head 31 as indicated generally by the arrow 38.

The source 36 is preferably of the penetrative radiation type wherein asource of beta, gamma, bremsstrahlung or other type radiation isproduced to irradiate the material to be measured. The radiationdetector in the detector head 31 may be a scintillation detector or anionization chamber which is effective to determine the amount ofradiation passing through the web W of material. The choice of radiationdepends on the character and the density of the material being measured.That is, a useful detector response results from the use of beta orbremsstrahlung radiation for light weight materials but there would besubstantially no absorption of a more penetrating radiation such asgamma. On the other hand, it is desirable to use a gamma source inmeasuring a relatively dense material. Typical examples of beta emittersare Strontium 90 and Krypton 85, while Americium 241 and Cesium 137 aresuitable gamma emitters.

Referring to FIGS. 35, a milled groove 39 is formed within the plate 34around the aperture 37 and forms a guideway for supporting a shutter 40having an outwardly projecting rib or flange 41 which projects into thegroove 39. Thus the shutter 40 is slidably supported for movementbetween a closed position, as shown in full lines, and an open positionwhere the shutter is retracted to the left in FIGS. 3 and 4 to open theaperture 37. In the closed position, the flange 41 on the forward end ofthe shutter 40 is received within the corresponding portion of thegroove 39 so that the cooperation between the interfitting flange 41 andthe groove 39 form an effective seal between the shutter 40 and theplate 34.

The shutter 40 is made of suitable material which resists exceedinglyhigh temperatures such as would occur in a fire and also forms aneffective shield to block radiation from the source 36. Suitablematerials for the shutter are defined in the Holben and Lehman patentsmentioned above.

Means for moving the shutter 40 within the guideway 39 to open theaperture 37 include a solenoid 50 which has its operating coil 51mounted on an extension plate 52 bolted to the under surface of theplate 34 by screws 53. The solenoid 50 has a T-shaped armature 55having, at its forward end, a pair of flanges 56 which receive avertically extending block 57 therebetween. The block 57 supports, atits upper end, a threaded rod 58 which extends generally in thedirection of movement of the solenoid armature. An arm 60 (FIG. 3) ismounted on the shutter 40 by screws 61 and depends downwardly to receivethe rod 58 projecting through a hole formed within the arm 60. A pair oflock nuts 63 are mounted on the bolt 58 on opposite sides of the arm 60and provide means for adjustably positioning the shutter 40 in relationto the solenoid armature 55.

The shutter 40 is moved to its closed position upon the deenergizationof the solenoid 50 by a pair of retraction or tension springs 65 eachhaving one end secured to the plate 34 by a spring retainer bracket 66(FIG. 4), The opposite ends of the spring 65 are connected to thesolenoid armature 55 by means of a hat bracket 70 which is secured tothe flanges 56 by a bolt 71 extending through aligned holes formedwithin the bracket 76, flanges 56 and block 57. Thus when the solenoidis energized, the assembly including the block 57, the shutter arm 60and the shutter 40 move to the left (FIG. 3) causing the extension ofthe springs 66 and the opening of the aperture 37. When the solenoid isdeenergized, the springs 66 return the shutter 40 to a position closingthe aperture 37 The invention includes means responsive to theoccurrence of a predetermined high temperature for deenergizing thesolenoid 50. Preferably this means comprises a heat sensitive orresponsive fuse 80 mounted on the plate 52 by suitable fuse clips 82 andwired in series with the coil 51. The heat responsive fuse 80 may be thetype TFX manufactured by Bussman Manufacturing Division of McGraw-EdisonCompany, of St. Louis, Missouri, and will interrupt the flow interruptthe flow of current to the solenoid when the ambient temperature reachesapproximately 300 F. The fuse 80 is provided in the event thatelectrical power to the solenoid still exists at this temperature,although it can be reasonably expected that by the time this temperaturehas occurred, either the solenoid itself will have become inoperative orthe electrical lines to the solenoid would have become disrupted orotherwise deenergized.

Referring more particularly to FIGS. 69, a cylindrical,transversely-aligned bore or opening 85 is formed within the plate 34and extends from a counterbore threaded portion 86 on an outside edgesurface of the plate 34 inwardly in intersecting relation with theshutter opening in the plate 34. Thus, the hole or bore 85 joinscoaxially and concentrically with a smaller diameter hole 88 which opensinto the groove 39 forming a portion of the shutter guideway, forming anannular inner abutment or shoulder 89 at the junction of the bore 85 andthe hole 88.

An elongated pin or plunger 90 is inserted through the larger open endof the bore 85 at the threaded portion 86 and has a stem-like elongatedcylindrical portion 91 extending into the hole 88. The portion 91 of theplunger 90 is of somewhat reduced diameter as compared to that of thehole 88. The forward end of the plunger 90 is terminated in a somewhaten larged cylindrical tip portion 92 which forms with the stem portion91 an annular, inwardly-facing shoulder 93. The diameter of the tipportion 92 is such that it forms a relatively loose fit when insertedwithin the hole 88.

A cylindrical collar 94 is formed on the inner end of the plunger 90 andhas an outer diameter which conforms approximately with that of the bore85 to form a relatively loose fit therewith. The collar 94 is formedwith a short inwardly-extending, spring-locating boss 96.

An annular, tapered, ring-like shoulder of a suitable eutectic alloy orsolder composition is formed on the plunger in surrounding relation to.an axial portion of the stem 91. The ring 95 is thus essentiallyfrustoconical in space with its base being formed in abutment with thecollar 94 and having a diameter at its base substantially greater thanthat of the hole 88. The outer frustoconical surface of the ring 95 isproportioned to engage the shoulder 89 and thus forms a block or abarrier which retains the plunger 90 and the tip portion 92 in aretracted or inner position. A compression coil spring 98 is positionedwithin the bore 85 and has its inner end located over the boss 96 and inabutment with the collar 94. The spring is retained in its compressed orstressed condition within the bore 85 by a plug 99 which is threadedinto the threaded counterbore 86 and engages the end of the spring.

A notch 100 having a diameter which is somewhat greater than that of thehole 88 is formed within the flange 41 of the shutter 40 and ispositioned to be in alignment with the hole 88 when the shutter 40 is inits closed posi ion. Referring to FIG. 8, a weep hole 102 extendsvertically upward from the underneath surface of the plate 34 inintersecting relation with the bore 85 and close to the position of thesolder ring 95.

As an example, the ring 95 may be formed of a solder compositionincluding approximately 95 percent tin, 3.5 percent silver and 1 percentantimony so that it has a eutectic melting temperature at approximately430 F. However, any metal alloy material may be used which hassufficient resistance against cold flow to hold its shape over extendedperiods of use at temperatures below the eutectic temperature, and whichmelts at a predetermined or predictable temperature to release theplunger 90 for locking movement into engagement with the shutter 40.

Thus when the ambient temperature surrounding the gauge increase toapproximately 300 F, the fuse 80 blows to break the circuit to thesolenoid so that the springs 65 move the shutter 40 to its closedposition. However, at this temperature, the power to the solenoid mayalready have been removed, and the fuse 80 accordingly acts as a backupor safety device to assure that the shutter closes.

If the ambient temperature continues to increase and reaches atemperature of approximately 430 F, the solder of the ring 95 melts andthe molten material flows outwardly through the weep hole 162. Themelting of the ring 95 thus removes the barrier holding the plunger 90in its retracted position and the spring 98 forces the tip portion 92 ofthe plunger 90 into the notch 100 formed within the shutter flange 41.As a result, the shutter 40 is positively locked in its closed position.As shown in FIG. 9, the plunger 90 will become canted or tilted in thehole 88 such as by mechanical jarring, or by slight movement of theshutter toward its open position, so that the shoulder 93 engages theplate 34 just outwardly of the hole 88, and prevents the plunger fromretracting even if the ambient temperature exceeds the point where thespring 98 loses its effectiveness.

The locking system constructed in accordance with the present inventionprovides a simple, dependable and economical means for locking theshutter in its closed position in the event of excessive heat such aswould occur in a fire. Thus, the shutter locking system of the presentinvention provides means for closing the shutter upon the attainment ofa first predetermined temperature by the blowing of the fuse 80 and theoperation of the retraction springs 65, followed by barrier means whichis removable upon the attainment of a second and higher predeterminedtemperature to permit a movable element to move into locking relationwith the shutter. In the locked position, all possibility of radiationbeing released by the accidental opening of the shutter after it hasbeen closed and locked as described above is eliminated.

The shutter locking system of this invention is entirely selfcontained,and while in the preferred embodiment it is shown as being incorporatedwithin the plate 34 comprising the guide for the shutter 40, it isobvious that the relative position of the parts can be reversed. Inother words, the movable parts of the locking mechanism could be placedwholly within the shutter 40, with the pin 90 moving outwardly intolocking engagement with the shutter guide.

It is also within the scope of this invention to employ any suitablemotor for the opening and closing of the shutter 40. Preferably, asingle acting motor is used, such as the solenoid disclosed, and it isalso within the scope of this invention to employ an air-operated motor,such as a piston motor. If an air motor is used, it will be deenergizedwhen the air supply line to the motor ruptures or breaks with heat. Ashort section of plastic tubing can conveniently be incorporated in theair line as an equivalent or of the fuse 80 used in this embodiment.

While the form of apparatus herein described constitutes a preferredembodiment of the invention, it is to be understood that the inventionis not limited to this precise form of apparatus, and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

Iclaim:

1. A nucleonic radiation measuring instrument comprising a housingenclosing a source of nuclear radiation and having an aperture forreleasing radiation from said housing for measurement purposes, ashutter for said aperture, means supporting said shutter for movementbetween an open position to release radiation from said aperture and aclosed position effectively confining the radiation within said housing,bias means urging said shutter to said closed position, motor means formoving said shutter from said closed position to said open position,means responsive to the occurrence of a first predetermined high ambienttemperature for deenergizing said motor means so that said bias meansmoves said shutter from said open position to said closed position, lockmeans associated with said shutter and including a member movablebetween a retracted position to permit movement of said shutter and anextended position locking said shutter in said closed position, meansurging said member toward said extended position, thermal responsivebarrier means retaining said member in said retracted position, andbeing responsive to a predetermined ambient temperature higher than saidfirst temperature for releasing said member for movement to saidextended position locking said shutter in said closed position.

2. An instrument as defined in claim 1 wherein said barrier meanscomprises a eutectic alloy having a predetermined melting point so thatsaid barrier means melts and flows to release said member when saidhigher temperature occurs.

3. An instrument as defined in claim 2 wherein said urging meanscomprises a spring normally held in a stressed condition and movableupon the melting of said barrier means to effect locking of said shutterin its said closed position.

4. An instrument as defined in claim 2 wherein said shutter includes anoutwardly projecting flange, said supporting means for said shutterincluding means defining a guideway receiving said flange, meansdefining an opening within said supporting means for said shutter, saidmember comprising a pin mounted for axial movement within said opening,said barrier means comprising a solder ring surrounding said pin, meansdefining a slot within said flange, and said slot being in alignmentwith said opening when said shutter is in said closed position forreceiving said pin.

5. An instrument as defined in claim 4 including means defining anannular shoulder within said opening formed within said supportingmeans, said solder ring having an outer surface engaging said shoulderfor retaining said pin in said retracted position, said urging meanscomprising a compression spring mounted within said opening and engagingsaid pin, and plug means for retaining said spring within said openmg.

6. An instrument as defined in claim 4 wherein said pin includes a headportion forming an external shoulder engageable with said supportingmeans at said opening for securing said pin in said extended position inresponse to slight movement of said shutter toward said open position.

'7. A nucleonic radiation energy measuring instrument having a source ofnuclear energy and incorporating a temperature responsive safety lock inwhich a shutter member is mounted on a guide member for movement betweena retracted position defining an opening for radiation measurementpurposes and a closed position effectively confining radiation from saidsource, the improvement in shutter locking mechanism comprising meansdefining an essentially rigid movable locking member mounted in one ofsaid shutter and guide members and being movable between a retractedposition permitting movement of said shutter member between its saidpositions, and an operative extended position in which said lockingmember is in locking engagement with the other of said shutter and guidemembers, and metal barrier means having a predetermined meltingtemperature retaining said locking member in its said retracted positionand flowable upon the attainment of said temperature to release saidlocking members for movement into its said operative position.

8. The instrument of claim 7 in which said locking member includes aspring normally held by said metal barrier in a stressed condition andreleased upon the melting of said barrier for moving said locking memberinto said operative position.

9. The instrument of claim 8 in which said locking member furthercomprises a plunger in said guide member, means forming a head on saidplunger, a recess formed in said shutter member aligned with said headin the closed position thereof, said head being proportioned to bereceived in said recess in its said operative position.

10. The instrument of claim 9 in which said metal barrier meanscomprises an annular ring of eutectic material carried on said plunger,and means in said guide defining a shoulder normally in engagement withsaid ring and permitting movement of said plunger therepast upon themelting of said ring.

1. A nucleonic radiation measuring instrument comprising a housingenclosing a source of nuclear radiation and having an aperture forreleasing radiation from said housing for measurement purposes, ashutter for said aperture, means supporting said shutter for movementbetween an open position to release radiation from said aperture and aclosed position effectively confining the radiation within said housing,bias means urging said shutter to said closed position, motor means formoving said shutter from said closed position to said open position,means responsive to the occurrence of a first predetermined high ambienttemperature for deenergizing said motor means so that said bias meansmoves said shutter from said open position to said closed position, lockmeans associated with said shutter and including a member movablebetween a retracted position to permit movement of said shutter and anextended position locking said shutter in said closed position, meansurging said member toward said extended position, thermal responsivebarrier means retaining said member in said retracted position, andbeing responsive to a predetermined ambient temperature higher than saidfirst temperature for releasing said member for movement to saidextended position locking said shutter in said closed position.
 2. Aninstrument as defined in claim 1 wherein said barrier means comprises aeutectic alloy having a predetermined melting point so that said barriermeans melts and flows to release said member when said highertemperature occurs.
 3. An instrument as defined in claim 2 wherein saidurging means comprises a spring normally held in a stressed conditionand movable upon the melting of said barrier means to effect locking ofsaid shutter in its said closed position.
 4. An instrument as defined inclaim 2 wherein said shutter includes an outwardly projecting flange,said supporting means for said shutter including means defining aguideway receiving said flange, means defining an opening within saidsupporting means for said shutter, said member comprising a pin mountedfor axial movement within said opening, said barrier means comprising asolder ring surrounding said pin, means defining a slot within saidflange, and said slot being in alignment with said opening when saidshutter is in said closed position for receiving said pin.
 5. Aninstrument as defined in claim 4 including means defining an annularshoulder within said opening formed within said supporting means, saidsolder ring having an outer surface engaging said shoulder for retainingsaid pin in said retracted position, said urging means comprising acompression spring mounted within said opening and engaging said pin,and plug means for retaining said spring within said opening.
 6. Aninstrument as defined in claim 4 wherein said pin includes a headportion forming an external shoulder engageable with said supportingmeans at said opening for securing said pin in said extended position inresponse to slight movement of said shutter toward said open position.7. A nucleonic radiation energy measuring instrument having a source ofnuclear energy and incorporating a temperature responsive safety lock inwhich a shutter member is mounted on a guide member for movement betweena retracted position defining an opening for radiation measurementpurposes and a closed position effectively confining radiation from saidsource, the improvement in shutter locking mechanism comprising meansdefining an essentially rigid movable locking member mounted in one ofsaid shutter and guide members and being movable between a retractedposition permitting movement of said shutter member between iTs saidpositions, and an operative extended position in which said lockingmember is in locking engagement with the other of said shutter and guidemembers, and metal barrier means having a predetermined meltingtemperature retaining said locking member in its said retracted positionand flowable upon the attainment of said temperature to release saidlocking members for movement into its said operative position.
 8. Theinstrument of claim 7 in which said locking member includes a springnormally held by said metal barrier in a stressed condition and releasedupon the melting of said barrier for moving said locking member intosaid operative position.
 9. The instrument of claim 8 in which saidlocking member further comprises a plunger in said guide member, meansforming a head on said plunger, a recess formed in said shutter memberaligned with said head in the closed position thereof, said head beingproportioned to be received in said recess in its said operativeposition.
 10. The instrument of claim 9 in which said metal barriermeans comprises an annular ring of eutectic material carried on saidplunger, and means in said guide defining a shoulder normally inengagement with said ring and permitting movement of said plungertherepast upon the melting of said ring.